A variety of liquid pumps are used to drive liquid samples in analytical systems. For example, for liquid chromatography (LC), a pump is used to drive liquid eluent through a stationary separation medium phase, such as a chromatography column packed with ion-exchange resin, and through connected devices that modify and/or monitor the effluent from the stationary phase. Such pumps preferably produce steady flow which is easily and precisely controllable. Also, separation media in the form of packed beds of small particles or beads can create high resistance to liquid flow. Thus, the pump should be capable of pumping against high back pressures, e.g., 1000 psi or more. A typical liquid chromatography pump is of the mechanical, dual-piston type that incorporates components such as pistons, seals, check valves, and the like. To meet and maintain the stringent requirements of long term use, e.g., use for tens of thousands of cycles, the moving and stationary components must be extremely durable. Thus, the pump design and material of construction and fabrication can be the most costly component in an LC system.
In the past, flow rates in LC have typically been about 1-2 ml/min. Newer methods employ separation columns of very small internal diameter (e.g., 100 to 400 μm) and operate the separation processes at very low flow rates (e.g., <10 μL/min). There is a need for a pump which can operate at such low flow rates which is (a) stable, and easily and precisely controllable, (b) capable of maintaining flow against high back pressures and (c) less expensive to build and more durable than conventional LC pumps.